Method of making an elastomeric film

ABSTRACT

This invention provides a process for preparing a heat shrinkable film by extruding a blend of elastomer, hydrocarbon oil and polyolefin to form a film, stretch orienting the film to form a stretched film, annealing the stretched film while still under stress, then cooling while further maintaining stress on the film. This invention further provides a process for preparing an elasticized composite material by attaching strips of the heat shrinkable film to a flexible substrate and then heating the composite.

This is a continuation of Ser. No. 469,758, filed Jan. 17,1990(abandoned) which is a continuation of Ser. No. 277,716, filed Nov. 30,1988 (abandoned) which is a division of Ser. No. 123,774, filed Nov. 23,1987 (now U.S. Pat. No. 4,820,590), which is a division of Ser. No.732,127, filed May 8, 1985 (now U.S. Pat. No. 4,714,735).

BACKGROUND OF THE INVENTION

This invention relates generally to the thermoplastic elastomers and inparticular, to the thermoplastic elastomers which have been thermallyoriented.

Thermoplastic elastomers possess properties of both thermoplastics andelastomers and have a wide range of applications. In certainapplications, a thermoplastic elastomer film is dimensionally stabilizedin a stretched condition (wherein stresses and strains in the film havebeen frozen in) for subsequent use. For example, the stretchedthermoplastic elastomer may be applied to a substrate and later heatedcausing the thermoplastic elastomer to shrink and retain substantialelastic properties. One such use is disclosed in European patentapplication No. 84301717.9 (Publication No. 0119825) wherein thestretched dimensionally stable thermoplastic elastomer is placed on adiaper waistband and reheated causing the thermoplastic elastomer tocontract and revert to a heat stable elastic state. The diaper thus, isprovided with a flexible and stretchable waistband. A similarapplication of thermoplastic elastomers is disclosed in European patentapplication No. 84301720.38 (Publication No. 0119827). Thesepublications are cited merely to disclose a possible use ofthermoplastic elastomers.

In many applications, particularly where the thermoplastic elastomer issecured to a substrate for later contraction by the application of heat,it is important that the thermoplastic elastomer have relatively highshrink force since the substrate resists shrinkage. The shrink force isdetermined by measuring the shrinkage of the film sample against anapplied force and is referred to herein as weighted shrink. The weightedshrink properties differ markedly from free shrinkage (no appliedweight) and hence is a key property in determining the suitability of aheat shrinkable film on substrates.

U.S. Pat. No. 4,303,571, issued to D. S. Jansen et al disclose athermoplastic elastomer film comprising 25 to 55 parts by weight of anethylene-propylene copolymer, 35 to 55 parts by weight of an EVAcopolymer and 15 to 25 parts by weight of a liquid hydrocarbon processoil.

As will be demonstrated in the discussion of the comparative examplescontained herein, the elastomeric film made from the compositiondisclosed in U.S. Pat. No. 4,303,571 possesses satisfactory shrinkproperties, but not nearly as good as those possessed by the compositionof the present invention, particularly with respect to weighted shrinkproperties.

A problem associated with thermoplastic elastomers is tackiness whichimpedes unwinding of the film during processing. This is a particularlyserious problem with film compositions containing EVA and processingoil. Moreover, addition of particulate antiblocks are not particularlyeffective in thermoplastic elastomers because of the difficulty indispersing the additives uniformly on the film surface, since theadditives tend to concentrate in the elastomer phase.

SUMMARY OF THE INVENTION

The present invention provides an improved film composition and processfor manufacturing which exhibits excellent shrink force and possessesnonblocking properties.

The film composition in one embodiment of the present inventioncomprises from 10 to 40 weight percent of an olefinic elastomer, notmore than 12 weight percent (preferably not more than 10 weight percent)of a normal liquid processing oil, and from 50 to 80 weight percent of athermoplastic ethylene copolymer, preferably vinyl acetate copolymer(EVA), all weight percents based on the weight of the three componentcomposition. The film is dimensionally stable in a stretched condition(draw ratio of 1.3:1 to 6:1) and is contractible to a thermally stableand elastic condition by the application of heat.

The method for preparing the thermoplastic elastomer film comprisesstretching the film at a temperature below the melting point of the EVAcomponent at a draw ratio between about 1.3:1 and 6:1, annealing thestretched film, and cooling of the film to ambient temperature. The filmmay be used by securing it to a substrate such as a inelasticthermoplastic or fabric, and heating the film to an elevated temperaturewhereby the film contracts to a thermally stable length and possesseselastic properties. The composite thus may be expanded by theapplication of tension which upon release returns to its original shape.

In another embodiment of the invention, the film comprises a compositeof one layer of a thermoplastic elastomer and a thin coating of anethylene polymer or copolymer having a relatively high Melt Index. Uponthe subsequent stretch orienting the composite, the coating becomes eventhinner. The thermoplastic elastomer layer is preferably the compositionas defined above, particularly if high shrink force is desired inaddition to antiblock properties. The coating preferably also containsparticulate antiblock additives, thus avoiding the difficult problem ofdistributing antiblock particles on or near the film surface.

The present invention contemplates (1) an improved stretch-oriented,dimensionally stable thermoplastic elastomer which is shrinkable uponapplication of heat, (2) a composite of the thermoplastic elastomer anda substrate wherein the orientation has been released by the applicationof heat, (3) a method of preparing the oriented thermoplastic elastomerfilm, (4) a method of manufacturing an elastic composite comprising athermoplastic elastomer and a substrate of inelastic material, (5) athermoplastic elastomer having a thin coating of a nonblocking polymerand (6) a method of preparing a nonblocking thermoplastic elastomer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing the present invention, it is necessary to use certaintechnical terms, some of which are commonly used in the industry andothers of which are defined herein to express a concept.

In order to avoid confusion, the following terms used herein shall havethe meaning indicated:

"Draw ratio"-the ratio of the final stabilized length (after orientationand "snapback") of an oriented film and the initial length of the filmbefore orientation. Draw ratio in unidirectional orientation is alsoequal to the ratio of the thickness of the stabilized oriented film andthe initial unoriented film.

"Shrink force"-the force required to prevent shrinkage of an orientedfilm by application of heat.

"Shrink stress"-the shrink force per unit area (g/cm²).

"Annealing"-a heat treatment process for reducing strains and stressesset up in the film during orientation. The process comprises maintainingthe film while in stretched condition at the annealing temperature, fora period of time, followed by cooling the film to room temperature.

"Thermoplastic elastomer"-frequently called rubbery thermoplastics, areblends of a thermoplastic material and elastomer that are processable asa melt, at elevated temperatures, but exhibit properties similar tovulcanized elastomers at room temperature.

"Melt Index" (MI)-g/10 min (ASTM-D 1238; condition E).

In its broadest form, the thermoplastic elastomer film composition ofthe present invention comprises three main components, (1) olefinicelastomer, (2) ethylene copolymer and (3) a hydrocarbon process oil.

The concentrations of the three components of the blend are as follows:

    ______________________________________                                                             Preferred   Most                                         Component                                                                              Concentration                                                                             Concentration                                                                             Preferred                                    ______________________________________                                        Olefinic 10-40   wt %    15-30 wt %  20-30 wt %                               Elastomer                                                                     Ethylene 50-80   wt %    60-80 wt %  65-75 wt %                               Copolymer                                                                     Process Oil                                                                            0-12    wt %    2-10  wt %  4-8   wt %                               ______________________________________                                    

The above concentration range may be combined in any permissiblecombination, although the particular combinations shown are preferred.For example, a preferred composition comprises 10-40 wt % elastomer,60-80 wt % ethylene copolymer, and 0-12 wt % process oil. The weightconcentration of each component is based on the total weight of thethree main components.

Elastomer Component: The olefinic elastomer component of the compositionpreferably comprises an ethylene copolymer elastomer, such as acopolymer of ethylene with higher alpha-olefin. Preferred ethyleneelastomer copolymers include EPM (ASTM D-1418-72a designation for anethylene-propylene elastomer copolymer) or EPDM (ASTM D-1418-72adesignation for an ethylene-propylene diene elastomer terpolymer). Alsousable are high molecular weight polyisobutylene, butyl rubbers andhalogenated butyl rubbers.

Preferred ethylene elastomer copolymers for use herein comprise from 30to 90 weight percent ethylene, more preferably from 35 to 80 weightpercent ethylene, and most preferably from 50 to 80 weight percentethylene and have a Mooney viscosity (ML 1+8 at °F. between 25 and 80).

EPDM is a terpolymer of ethylene, a higher alpha-olefin such aspropylene, and a nonconjugated diene. In such elastomers, thenonconjugated diolefin may be straight chain, branched chain or cyclichydrocarbon diolefins having from 6 to 15 carbon atoms.

Of the nonconjugated dienes typically used to prepare these copolymers,preferred are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norborneneand 5-ethylidene-2-norbornene; 5-ethylidene-2-norbornene (ENB) and1,4-hexadiene are particularly preferred diolefins. EPDM elastomers andtheir method of manufacture are well known to those skilled in the art.Oil extended EPDM elastomers may also be used. Preferred EPDM elastomerscontain from 30 to 90 weight percent ethylene and most preferably from50 to 80 weight percent ethylene, and from 0.5 to 15 weight percent ofthe nonconjugated diolefin.

As mentioned above, the olefinic elastomer useful in this invention mayalso be a polyisobutylene, a copolymer of isobutylene and isoprene(generalLy known as butyl rubber) or a halogenated copolymer ofisobutylene and isoprene (generally known as halogenated butyl rubber,such as chlorinated, brominated and chlorobrominated butyl rubber).Butyl rubber is a vulcanizable rubber copolymer containing from 85 to99.5 percent combined isoolefin having from 4 to 8 carbon atoms and from0.5 to 15 percent combined conjugated diolefin having from 4 to 8 carbonatoms. Such copolymers and their preparation are well known, andgenerally the isoolefin is a compound such as isobutylene and thediolefin is a compound such as butadiene or isoprene. Halogenated butylrubbers are also well known: chlorinated and brominated butyl rubbergenerally contains from 1.0 to 3.0 weight percent bromine and from 0.05to 0.5 weight percent chlorine.

Ethylene Copolymer Component: The ethylene copolymers include those ofethylene and alpha-olefins having 3 to 16 carbon atoms such as propyleneor 1-butene. Also included are copolymers of ethylene with unsaturatedesters of a lower carboxylic acid or with an unsaturated carboxylicacid. In particular, copolymers of ethylene with vinyl acetate (EVA), orwith acrylic acid (EAA), or methacrylic acid (EMA), are preferred. Theethylene copolymers to be employed generally contain from 50 to 99weight percent ethylene, most preferably from 60 to 95 weight percentethylene.

The most preferred ethylene copolymer useful in the present invention isEVA. The EVA may have a vinyl acetate (VA) content between about 9% and40% by weight, with about 15 to 35 weight percent VA being preferred.

VA contents below about 9 wt % do not possess sufficient flexibility andorientability for purposes of the present invention and VA contentsabove 40 wt % exhibit excessive tackiness. The best balance oforientability and non-tackiness occurs at VA contents between 15 and 35wt %.

Preferred Melt Index (ASTM-D-1238, Condition E) for EVA is from 1 to 20,with 2 to 10 being most preferred.

The ethylene copolymer component normally will determine the operatingtemperatures of the tentering and annealing operations. These operationsmay be carried out at temperatures not less than 100° F. and below(preferably not more than 10° F. below) the crystalline melting point ofthe ethylene copolymer component. The annealing step preferably is at±20° F. of the orienting temperature. The crystalline melting point ofEVA ranges from approximately 105° F. and 200° F., depending on the VAcontent and MI, with the preferred EVA's having crystalline meltingpoints between about 130° F. and 160° F. For economics, orientingtemperatures of 160° F. and below are preferred.

Process Oil Component: Hydrocarbon oils useful in the present inventionfunction as process aids whose activity is enhanced in the presence ofvinyl acetate copolymers, as plasticizers producing low modulus andenhanced elasticity in the solid state and those useful are the normallyliquid hydrocarbon processing and extender oils (ASTM D 2226)categorized as aromatic, highly aromatic, naphthenic and paraffinicprocess oils of a medium viscosity range. Oils sold under the trademarks"FLEXON" (aromatic petroleum oil) and "SUNPAR" (paraffinic oil) havebeen found especially useful.

Other Additives: The composition may also include a filler material, anantiblock agent, processing aids, stabilizers and other conventionaladditives.

FILM PREPARATION

Resin/Blend Preparation: Preparation of compositions usable in thisinvention can be achieved in several different ways. The variouscomponents may be brought into intimate contact by, for example, dryblending these materials and then passing the overall compositionthrough a compounding extruder. Alternatively, the components may be feddirectly to a mixing device such as a compounding extruder, high shearcontinuous mixer, two roll mill or an internal mixer such as a BANBURY(high intensity, twin-screw) mixer. The optional ingredients previouslydescribed can be added to the composition during this mixing operation .Overall, the objective is to obtain a uniform dispersion of allingredients and this is readily achieved by inducing sufficient shearand heat to cause the plastics component(s) to melt. However, time andtemperature of mixing should be controlled as is normally done by oneskilled in the art so as to avoid molecular weight degradation.

Film Extrusion: Film from the resin compound may be manufactured byconventional tubular extrusion, (blown bubble process) or by castextrusion, with the latter being preferred. In the cast extrusionprocess, the molten resin is extruded from an elongate die to the formof a web. The web is cast onto a chill roller, which solidifies thepolymer, and finally wound into a roll.

The extrusion temperatures, die temperatures, and chill rolltemperatures will depend on the composition employed, but generally willbe in the following ranges for the compositions of the present inventionprepared by cast extrusion:

Melt Temperature (° F.): 350-450

Die Temperature (° F.): 350-450

Chill Roll Temperature (° F.): 70-130

The process described above may also include a set of embossing rolls tochill and form the film.

Orientation: Orientation of the film may be carried out in the machinedirection (MD) or the transverse direction (TD) or both directions(biaxially) using conventional equipment and processes.

For orientation in the MD, a polymeric film at an elevated temperature(but below the crystalline melting point of the polymer) is passed froma feed roll of film around two rollers driven at different surfacespeeds and finally to a takeup roller. The driven roller closest to thetakeup roll is driven faster than the driven roller closest to the feedroll, such that the film is stretched between the driven rollers. Theassembly may include a roller intermediate the second roller and takeuproller to cool the film. The second roller and the takeup roller may bedriven at the same peripheral speeds to maintain the film in thestretched condition. If supplementary cooling is not used, the film willcool to ambient temperature on the take up roll.

The degree of stretch will depend upon the relative peripheral speeds ofthe driven rollers and the distance between the rollers. Stretch ratesof 50 to 500 percent/minute will be satisfactory for most MD orientationapplications.

Preferably, however, film orientation will be carried out in a tenteringdevice to impart TD orientation to the film. The film is cast asdescribed above or is unwound from a film roll and then gripped by theedges for processing through the orientation steps. The film is passedsuccessively through a preheat step, a stretching step at elevatedtemperatures (e.g. from 100° F. to a temperature slightly below thecrystalline melting point of the ethylene copolymer), an annealing step,and finally a cooling step. (Although cooling may be considered part ofthe annealing step, for convenience it is described as a separate stepherein.) The preheat, orientation, and a portion of the annealingtemperature is controlled at an elevated temperature but below thecrystalline melting point of the polymer. Although not essential, it ispreferred that tension be maintained on the film during the annealingand cooling steps to minimize shrinkback. Upon cooling to ambienttemperature (i.e., room temperature) or near ambient, the holding forcemay be released. The film may contract somewhat (snapback) in the TD butwill retain substantial portion of its stretched length.

The tenter operating conditions can vary within relatively wide rangesand will depend on the several variables including film composition,film thickness, degree of orientation desired, annealing conditions,etc. The following is exemplary of a process for stretching 100 micronthick film (containing EVA) from 24 inches wide to a final width ofabout 60 inches, using a tenter manufactured by Marshall and WilliamsCompany of Providence, R.I.

ESTIMATED FILM RANGE

    ______________________________________                                        ESTIMATED FILM RANGE                                                                                              Approximate                               Step    Broad     Preferred Typical Time (Sec.)                               ______________________________________                                        Preheat 100-160° F.                                                                      115-140° F.                                                                      125° F.                                                                        3.0                                       Stretching                                                                            100-160° F.                                                                      115-140° F.                                                                      125° F.                                                                        9.0                                       Annealing                                                                             100-160° F.                                                                      110-150° F.                                                                      120° F.                                                                        3.0                                       Cooling Ambient   Ambient   Ambient 6.0                                       ______________________________________                                    

As indicated earlier, it is highly desirable to employ an annealing stepin the process. Annealing partially relieves the internal stress in thestretched film and dimensionally stabilizes the film for storage. It hasbeen found that by annealing the film at a temperature of ±40° F.,preferably ±20° F. of the orientation temperature (but slightly belowthe crystalline melting point of the ethylene copolymer) eliminatesundesirable shrinkage during storage. The preferred annealingtemperature is between 110° F. and 130° F. Temperatures which result inexcessive stress relieving should be avoided, since substantial frozenin stresses and strains should remain after the process is completed.

Annealing can be accomplished by maintaining the film in the stretchedcondition at the annealing temperature. Preferably, however, theannealing and cooling is carried out while permitting the film tocontract slightly, but still under stress. The guide rails of the tentercan be arranged in a converging manner to provide the annealing andcooling while the film contracts. The controlled shrinkback of from 5 to30%, preferably between 15 and 25%, of the maximum stretched width hasgiven particularly good results in eliminating storage shrinkage. Thisannealing and preshrinking removes some of the film stresses and strainsso that shrinkage will not occur at storage temperature. However, theannealing and cooling does not remove all the frozen in stress andstrain, since upon heating to elevated temperatures above storagetemperature the film will shrink.

The degree of stretching may vary within wide ranges. Draw ratios of1.3:1 to 6:1 are possible with 2:1 to 4:1 being preferred for TDtentering. The actual stretching will occur at higher ratios (1:5 to9:1) to allow for controlled shrinkage and snapback.

EXAMPLES

In order to demonstrate the effectiveness of the present invention,particularly in respect of improved shrink force and nonblockingproperties, a series of experiments were conducted comparing performanceof the film of the present invention with that of the prior art (U.S.Pat. No. 4,303,571).

Film Samples

Samples having the compositions listed in Table I were prepared byblending in the weight concentrations indicated using a BANBURY mixer.Each composition also included 6 wt % ethylene acrylic acid copolymerand filler material (CaCO₃). The resin blend was cast extruded into 150micron (approx.) thick film using 3" extruder and 30" wide flat die.

Properties of the Film

Each film sample was then tested for orientation/shrinkage propertieswith an Instron (Model 1122) in a temperature controlled chamber. Oneinch wide strips (cut in the TD) were taken from each sample, markedwith lines 4 cm apart and then drawn to 9 cm at 10 cm/minute at anelevated temperature (140° and 145° F.). After orientation, eachstretched film was quenched with water and removed from the Instron. Sixfilm strips were drawn for each formulation and the test was run inrandom order in blocks of nine to eliminate systematic test error.

For each formulation, 6 strips were heated in the oven for three minutesat 150° F.; three strips with a fixed weight and the other three stripsfreely suspended. The film strips were removed from the oven, allowed tocool and then measured to determine the % recovery.

The % recovery was calculated by the following formula: ##EQU1##

Table II presents the results, comparing the three sample average foreach formulation of the present invention (Samples A, B and C) with thethree sample average of each formulation of the prior art (Samples D, Eand F.).

As revealed in Table II, the percent recovery under restrainedconditions Samples A, B and C was higher than that of Samples D, E, andF. Percent restrained recovery for the A, B, C sample group averaged86.4%, whereas that of D, E F group averaged 82.3%. The shrink force,which is the force required to keep the film from shrinking can becalculated from these data. As shown in Table II, the shrink force forSamples A, B and C was substantially higher than that for Samples D, E,and F. Samples A and B exhibited particularly improved shrink force.

The higher shrink force of the Samples A, B and C permits use of athinner gauge film at the same draw ratio as demonstrated by thefollowing experiments.

Additional experiments were conducted to demonstrate shrinkage as afunction of restraining force and shrinkage temperature. Two orientedfilms having the compositions of Samples A and D were prepared using aMarshall and Williams Tenter operated under typical conditions describedin the Orientation section hereof. Each film thus was processed asfollows:

    ______________________________________                                                   Sample A    Sample D                                               ______________________________________                                        Initial Length                                                                             22.5   inches     22.5 inches                                    Stretch Length                                                                             66     inches     66   inches                                    Controlled Shrinkback                                                                      60     inches     60   inches                                    Length                                                                        Final Stabilized                                                                           50     inches     50   inches                                    Length                                                                        Film Gauge (Initial)                                                                       102    microns (avg)                                                                            146  microns (avg)                             Film Gauge (Final)                                                                         42     microns (avg)                                                                            58   microns (avg)                             Draw Ratio (Initial                                                                        2.42              2.51                                           Film Gauge/Final                                                              Film Gauge)                                                                   ______________________________________                                    

Strips (three for each test) of each film sample were taken andsubjected to shrinkage in an oven at a controlled temperature (120° F.or 150° F.) and at the following restraining forces: 0, 12 g, 24 g, 36g, 48 g and 60 g. Each strip was permitted to shrink for three minutesTable III presents the three-strip average for each test. These datademonstrate that the shrink stress for the composition of the presentinvention was substantially higher than the composition of the priorart. Moreover, the shrink force for Sample A strips exhibitedsubstantially higher shrink force than the Sample D strips, even thoughthe latter strips were substantially thicker in gauge hence larger crosssectional area) than the former strips.

It is preferred that the thermoplastic elastomer film on the presentinvention have a shrink stress of at least 5,000 g/cm² at theorientation temperature, thereby providing sufficient force for itsintended purpose. It is also preferred that the shrink force at 150° F.be at least 5,000 g/cm².

It is interesting to note from the Table III data that the shrinkage isgenerally linear with respect to the applied force. This permitscalculating the shrink force and shrink stress. Note that the shrinktemperature of 150° F. is higher than the orientation temperature and120° F. is lower than that temperature. The higher temperature resultsin more shrinkage since more stresses are relieved.

Antiblock Properties

The composition of the present invention also exhibits good antiblockingproperties in comparison to films of the compositions of samples D, Eand F.

Multi-layers of each film Sample A, B, C, D, E and F compositions (150micron thick unoriented) were stored for several weeks. The films werethen manually separated and subjectively rated for blocking (i.e.,resistance to unwinding).

    ______________________________________                                        Sample           Observed Blocking                                            ______________________________________                                        A                No blocking                                                  B                Slight tackiness                                             C                No blocking                                                  D                Fully Blocked                                                E                Partial Blocking                                             F                Partial Blocking                                             ______________________________________                                    

Antiblock property is important in unwinding the film during tenteringor during unwinding the oriented film of use. Sticking of the film isundesirable since it slows down the operation or renders the processinoperable.

THERMOPLASTIC ELASTOMER WITH COATING

Another embodiment of the present invention is directed specifically atsolving blocking associated with thermoplastic elastomers, particularlythose containing process oil and for high VA, ethylene vinyl acetate.These films are tacky by nature and require antiblock agents such asparticulate silica. The elastomer present in these blends appears toprevent uniform distribution of particulate antiblock in the resin withthe result that the antiblock does not become uniformly distributed onthe film surface.

In one aspect of this invention, a thin coating of an ethylene polymeror copolymer is provided on one or both sides of the base thermoplasticelastomer (core). The subsequent stretching of the film further reducesthe thickness of the coating. The coating thickness ratio(final/initial) is in proportion to the draw ratio. Preferably thecoating comprises conventional low density polyethylene (LDPE) having ahigh Melt Index (in excess of 3.0). Other ethylene polymers andcopolymers that may be used as the coating include linear low densitypolyethylenes (LLDPE), EVA, etc. These materials should have relativelyhigh Melt Indices (in excess of 3.0, preferably 5.0-30.0) and should becapable of high draw down, making them suitable for coextrusion with thebase resin (core layer), and should possess nontacky properties or betreatable to a nontacky condition (e.g. addition of antiblock).Coextrusion is the preferred coating method, but extrusion coating mayalso be used.

It is essential that the coating be sufficiently thin to avoidinterference with the shrink and elastic properties of the thermoplasticelastomer but sufficiently thick to impart antiblock properties to thecomposite. This latter requirement means that the coating must becapable of carrying uniformly distributed therein particulate finelydivided antiblock agent.

As applied to the core or base resin, the coating will comprise between2 to 15, preferably 2 to 10 weight percent of the composite and not morethan 25 microns thick. Following the orientation, the coating will bereduced to a thickness of not more than 7 microns and as thin aspossible. Preferred thickness after orientation is between 1 and 5microns.

The amount of antiblock in the coating may range from 500 to 5,000 ppm,with 1,000 to 4,000 being preferred. The coating may also include slipagents such as erucamide and oleamide.

The coating may be applied to only one side of the base resin butpreferably is applied to both sides.

It should be noted that the invention comprising the coating embodimentis not restricted to the thermoplastic elastomer composition specifiedin the earlier description of the "Elastomer Component" as the core(although these compositions are the most preferred) but may insteadcontemplate the use of any thermoplastic elastomer resin composition.The preferred resin composition comprises from 10 to 55 wt % of theelastomer component, from 35 to 80 wt % of the EVA component, and from 2to 25 wt % of the processing oil component.

OPERATION

In practice, the process of the present invention may be carried outusing an in-line operation wherein the extruder and orientation system(e.g., tenter) are arranged in tandem to form the film by casting ormelt embossing followed by film orientation. Alternatively, theseoperations may be carried out separately.

In a preferred embodiment, the compounded resin containing the threemain ingredients along with the other additives is introduced into anextruder and extruded into a web from a flat or coathanger type die andmelt embossed through counter rotating chill roll and embossing rolls.The film thickness may vary from 50 to 400 microns before orientationand from 10 to 200 microns after orientation. Preferably the film willhave a final stabilized thickness of between 10 and 100 microns afterorientation and annealing. The film is wound on a take up roll andtransferred to tentering equipment or processed in line with the tenter.

The edges of the film are gripped in the tentering equipment and passedsuccessively through (a) a preheat stage, (b) an expansion stage whereinthe film is stretched laterally at an elevated temperature, (c) anannealing stage and, finally, (d) a cooling stage where the stretchedfilm is cooled to near ambient temperature. Once the restraining forceis released, the film snaps back slightly but retains most of itsstretched length. This film is wound on a take up roll, ready fortransport or use.

The dimensionally stable film may be secured to a flexible substrate andheated causing it to shrink. Shrinkage commences at a few degrees abovestorage temperature, reaching maximum at some temperature above theorientation temperature.

In the embodiment for the coating of a thermoplastic elastomer, theoperation may be the same as above except that in extrusion of the resinto form the film, a coextrusion die may be used to apply the thincoating on one or both sides of the thermoplastic elastomer core.

In either embodiment, the film produced has excellent shrink forceproperties and good antiblock properties.

In another embodiment the invention comprises a process for preparing anelasticized composite material which comprises

(a) stretch orienting a film having a thickness of between 50 and 400microns and a composition of

(i) from 15 to 30 weight percent of an EPM or EPDM elastomer;

(ii) from 60 to 80 weight percent of an ethylene vinyl acetate copolymer(EVA) having a vinyl acetate content of about 9 to 40 weight percent;and

(iii) from 2 to 10 weight percent of a normally liquid hydrocarbonprocess oil;

by drawing the film in the transverse direction from 1.5 to 9 times itsoriginal length at a temperature not less than 100° F. and below thecrystalline melting point of the EVA;

(b) annealing the film at an annealing temperature of ±20° F. of theorientation temperature while maintaining a stress on the film;

(c) cooling the film to room temperature;

(d) securing a strip of the film to a layer of flexible, substantiallyinelastic material at longitudinally spaced locations along the film toform a composite;

(e) heating the composite to a temperature in excess of 100° F. towithin ±20° F. of the orienting temperature whereby the film and thelayer of flexible, substantially inelastic material contract to anelastic heat stable condition.

                                      TABLE I                                     __________________________________________________________________________           FILM SAMPLE          COMPARATIVE FILM SAMPLES                          Component                                                                            A      B      C      D      E      F                                   __________________________________________________________________________    Elastomer.sup.1                                                                      22.6                                                                             wt %                                                                              27.0                                                                             wt %                                                                              39.4                                                                             wt %                                                                              39.4                                                                             wt %                                                                              22.6                                                                             wt %                                                                              27.0                                                                             wt %                             EVA.sup.2                                                                            71.7                                                                             wt %                                                                              66.2                                                                             wt %                                                                              55.0                                                                             wt %                                                                              41.6                                                                             wt %                                                                              58.4                                                                             wt %                                                                              49.6                                                                             wt %                             Process Oil.sup.3                                                                    5.6                                                                              wt %                                                                              6.8                                                                              wt %                                                                              5.6                                                                              wt %                                                                              19.0                                                                             wt %                                                                              19.0                                                                             wt %                                                                              23.4                                                                             wt %                             MI     3.25   2.63   2.16   2.66   6.6    10.3                                __________________________________________________________________________     .sup.1 Ethylenepropylene copolymer rubber marketed as Vistalon 3708 by        Exxon Chemical Company.                                                       .sup.2 LD767 (28 wt % VA) sold by Exxon Chemical Company.                     .sup.3 Arco Prime 350 sold by Arco Chemical Company.                     

                                      TABLE II                                    __________________________________________________________________________              Initial                    Calculated                                         Gauge                                                                              Initial                                                                              Final  % Recovery                                                                            Shrink Force                             Sample                                                                            Test  (microns)                                                                          Length (cm)                                                                          Length (cm)                                                                          (Actual Draw)                                                                         (grams)                                  __________________________________________________________________________    A   Free  157.5                                                                              8.0    4.3    91.6    222                                          Restrained                                                                          149.9                                                                              8.0    4.5    87.5                                             B   Free  157.5                                                                              8.0    4.4    90.0    450                                          Restrained                                                                          157.5                                                                              8.0    4.5    86.8                                             C   Free  152.4                                                                              8.0    4.4    89.9    169                                          Restrained                                                                          154.9                                                                              7.9    4.6    85.6                                             D   Free  152.4                                                                              8.1    4.3    91.9    134                                          Restrained                                                                          149.9                                                                              8.2    4.7    82.2                                             E   Free  160.0                                                                              7.9    4.3    91.5    148                                          Restrained                                                                          162.6                                                                              8.0    4.7    82.6                                             F   Free  157.18                                                                             8.1    4.4    88.5    127                                          Restrained                                                                          152.4                                                                              8.1    4.7    81.3                                             __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________                                   Shrink    Shrink                                            Strip Length after shrinkage (cm)                                                               Force Area                                                                              Stress                               Restraining Force (grams)                                                                  0  12 24 36 48 60 (grams)**                                                                           (cm.sup.2)                                                                        g/cm.sup.2                           __________________________________________________________________________    Sample A*                                                                            120° F.                                                                      8.08                                                                             8.33                                                                             5.62                                                                             8.89                                                                             9.08                                                                             9.33                                                                             91    .010                                                                              9,100                                       150° F.                                                                      5.83                                                                             6.26                                                                             6.98                                                                             7.73                                                                             8.38                                                                             9.43                                                                             73    .011                                                                              6,636                                Sample D*                                                                            120° F.                                                                      8.57                                                                             8.82                                                                             9.15                                                                             9.41                                                                             9.74                                                                             10.01                                                                            59    .014                                                                              4,214                                       150° F.                                                                      5.73                                                                             6.23                                                                             6.91                                                                             7.90                                                                             8.75                                                                             10.04                                                                            65    .016                                                                              4,063                                __________________________________________________________________________     *three strip sample average                                                   **calculated                                                             

What is claimed is:
 1. A process for preparing a heat shrinkable filmcomprising:(a) extruding a molten blend comprising(i) from 10 to 40weight percent elastomer; (ii) 10 weight percent or less of ahydrocarbon oil; and (iii) from 50 to 80 weight percent of athermoplastic ethylene copolymer having a crystalline melting point; toform a film; (b) stretch orienting the film in a transverse directionfrom 1.5 to 9 times its original width at a temperature between 100° F.and 10° F. below the crystalline melting point of the ethylenecopolymer; (c) annealing the stretched film while the film is understress; and (d) cooling the film while maintaining stress on the film.2. A process as defined in claim 1 wherein the ethylene copolymer isselected from the group consisting of ethylene vinyl acetate, ethyleneacrylic acid and ethylene methacrylic acid.
 3. A process as defined inclaim 2 wherein the ethylene copolymer is ethylene vinyl acetate.
 4. Aprocess as defined in claim 3 wherein the annealing step is carried outwhile the film is under stress at a temperature between 20° F. above and20° F. below the stretch orienting temperature.
 5. A process as definedin claim 4 wherein the annealing and cooling steps are carried out bypermitting the film to shrink in a transverse direction by 30% or lessof the width of the film after stretch orienting.
 6. A process asdefined in claim 1 wherein the stretch orientation stretches the film bybetween 2 to 4 times its original width in the transverse direction. 7.A process for preparing a heat shrinkable film which comprises:(a)stretch orienting a film having a thickness of between 50 and 400microns and a composition of(i) from 15 to 30 weight percent of anethylene-propylene elastomer copolymer or an ethylene-propylene dieneelastomer terpolymer; (ii) from 60 to 80 weight percent of an ethylenevinyl acetate copolymer having a crystalline melting point and having avinyl acetate content of about 15 to 35 weight percent; and (iii) from 2to 10 weight percent of a normally liquid hydrocarbon process oil; bydrawing the film in a transverse direction from 1.5 to 9 times itsoriginal width at an orienting temperature of from 100° F. to thecrystalline melting point of the ethylene vinyl acetate; (b) annealingthe film at an annealing temperature between 40° F. above and 40° F.below the orienting temperature but less than the crystalline meltingpoint of the ethylene vinyl acetate while the film is under stress; and(c) cooling the film while maintaining stress on the film during atleast a portion of the cooling.
 8. A process as define din claim 7wherein the annealing step is carried out at a temperature between 20°F. above and 20° F. below the orienting temperature wherein the film ispermitted to shrink from its fully stretched width by 30% or less.
 9. Aprocess of making a heat shrinkable composite film having improvedantiblock properties comprising:(a) preparing a film of from 50 to 400microns thickness from a thermoplastic elastomer resin compositioncomprising from 10 to 40 weight percent of an elastomer, from 50 to 80weight percent of a thermoplastic polyolefin having a crystallinemelting point and 10 weight percent or less of a processing oil; (b)coextruding with said film a layer of a polymer selected from the groupconsisting of ethylene polymer and ethylene copolymer to form acomposite, said polymer having a melt index of at least 3.0,constituting from 2 to 15 weight percent of the composite and having athickness of 25 microns or less; (c) stretch orienting the composite ata temperature between 100° F. and 10° F. below the crystalline meltingpoint of the polyolefin at a draw ratio between 1.5:1 and 9:1 such thatthe layer thickness is 7 microns or less; and (d) cooling the stretchedcomposite to form a dimensionally stable elastomeric composite, saiddimensionally stable elastomeric composite being heat shrinkable.
 10. Aprocess as defined in claim 1 and comprising the additional steps ofadhering the heat shrinkable film to an inelastic substrate and heatingto cause said film to shrink, drawing the inelastic substrate with it.11. A process of making an elasticized composite material whichcomprises:(a) stretch orienting a film having a thickness of between 50and 400 microns and a composition of(i) from 15 to 30 weight percent ofan ethylene-propylene elastomer copolymer or an ethylene-propylene dieneelastomer terpolymer; (ii) from 60 to 80 weight percent of an ethylenevinyl acetate copolymer having a crystalline melting point and having avinyl acetate content of about 9 to 40 weight percent; and (iii) from 2to 10 weight percent of a normally liquid hydrocarbon processing oil; bydrawing the film in a transverse direction from 1.5 to 9 times itsoriginal width at an orienting temperature between 100° F. and thecrystalline melting point of the ethylene vinyl acetate; (b) annealingthe film at an annealing temperature between 20° F. above and 20° F.below the orienting temperature while the film is under stress; (c)cooling the film to room temperature; (d) securing a strip of the filmto a layer of flexible, substantially inelastic material atlongitudinally spaced locations along the film to form a composite; and(e) heating the composite to a temperature between 100° F. and 20° F.above the orienting temperature whereby the film and the layer offlexible, substantially inelastic material contract to an elastic heatstable condition.
 12. A process as defined in claim 7 wherein theorienting temperature and annealing temperature are between 100° F. and160° F.